Network initiated CS services during IMS call

ABSTRACT

An interruption of a call which is established or which is currently being established via an internet protocol domain of a mobile network may be avoided during a handling of a circuit switched signaling service to be terminated to a terminal and being different from a mobile terminating location request service.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. application Ser. No. 14/785,743, which hasa section 371(c) date of Oct. 20, 2015 (published as U.S. 20160072852)and which is the section 371 national stage application of internationalpatent application no. PCT/EP2013/062383, filed on Jun. 14, 2013, whichclaims priority to U.S. provisional application No. 61/808,394, filed onApr. 4, 2013. The above identified applications and publication areincorporated by this reference.

TECHNICAL FIELD

The present embodiments relate to telecommunications, and in particularto handling of a termination of a terminating circuit switched signalingservice to a terminal via a circuit switched access of a mobile network.Methods, nodes, a terminal, a communication system, and computerprograms are also described.

BACKGROUND

Third Partnership Project (3GPP) Technical Specification (TS) 23.272V11.4.0 (2013-03) defines that a terminal connected to a mobile networkperforms a Circuit Switched Fallback (CSFB) procedure in case of aNetwork (NW)-initiated circuit switched signaling service. The latterdocument also defines the handling of a Mobile Terminating LocationRequest (MT-LR) signaling service in a case in which an InternetProtocol (IP) Multimedia Subsystem (IMS) voice call is on-going.

SUMMARY

It is an object of the invention to provide measures with which aninterruption of a call which is established or which is currently beingestablished via an internet protocol domain of a mobile network may beavoided during a handling of a circuit switched signaling service to beterminated to a terminal and being different from a mobile terminatinglocation request service. It is also an object of the invention toprovide corresponding methods, nodes, a corresponding terminal, acorresponding communication system and corresponding computer programs.

The objects defined above are solved by methods comprising the featuresof embodiment 1, 6 or 15, a control node comprising the features ofembodiment 18, a terminal comprising the features of embodiment 20 or22, a communication system comprising the features of embodiment 24, andcomputer programs comprising the features of embodiment 25.

According to an exemplary aspect of the invention, a method to be usedin association with terminating a circuit switched signaling service toa terminal via a circuit switched access of a mobile network isprovided. The signaling service is different from a voice call via thecircuit switched access and from a mobile terminating location requestservice. A call via an internet protocol domain of the mobile networkand a packet switched access of the mobile network is or is beingestablished for the terminal. The method is performed by a control nodeof the mobile network. The method comprises receiving a paging requestfor paging the terminal via the packet switched access. The pagingrequest is for the circuit switched signaling service. The methodcomprises determining whether a call via the internet protocol domainand the packet switched access is or is being established for theterminal depending on the received paging request. The method comprisessending a paging rejection for rejecting the received paging requestdepending on the call via the internet protocol domain and the packetswitched access is or is being established for the terminal and sending,via the packet switched access, a paging request for paging the terminaldepending on the call via the internet protocol domain and the packetswitched access is not or is being not established for the terminal.

According to another exemplary aspect of the invention, a method to beused in association with terminating a circuit switched signalingservice to a terminal via a circuit switched access of a mobile networkis provided. The signaling service is different from a voice call viathe circuit switched access and from a mobile terminating locationrequest service. A call via an internet protocol domain of the mobilenetwork and a packet switched access of the mobile network is or isbeing established for the terminal. The method is performed by theterminal and comprises receiving, via the packet switched access, apaging request for paging the terminal. The paging request is for thecircuit switched signaling service. The method comprises determiningwhether a call via the internet protocol domain and the packet switchedaccess is or is being established for the terminal depending on thereceived paging request. The method comprises sending, via the packetswitched access, a paging rejection for rejecting the paging request bythe terminal depending on the call via the internet protocol domain andthe packet switched access is or is being established for the terminaland sending a paging response for accepting the paging request by theterminal depending on the call via the internet protocol domain and thepacket switched access is not or is being not established for theterminal.

According to another exemplary aspect of the invention, a method to beused in association with terminating a circuit switched signalingservice to a terminal via a circuit switched access of a mobile networkis provided. The signaling service is different from a voice call viathe circuit switched access and from a mobile terminating locationrequest service. A call via an internet protocol domain of the mobilenetwork and a packet switched access of the mobile network is or isbeing established for the terminal. The method is performed by theterminal and comprises receiving a paging request for paging theterminal via the packet switched access. The paging request is for thecircuit switched signaling service. The method comprises determiningwhether a signaling service via the internet protocol domain isavailable for the terminal depending on the received paging request. Thesignaling service via the internet protocol domain corresponds to thecircuit switched signaling service. The method comprises sending, viathe packet switched access, a support indication indicating a terminalsupport for the signaling service via the internet protocol domaindepending on the signaling service via the internet protocol domainbeing available for the terminal.

According to another exemplary aspect of the invention, a control nodefor a mobile network is provided. The control node is usable inassociation with terminating a circuit switched signaling service to aterminal via a circuit switched access of a mobile network. Thesignaling service is different from a voice call via the circuitswitched access and from a mobile terminating location request service.A call via an internet protocol domain of the mobile network and apacket switched access of the mobile network is or is being establishedfor the terminal. The control node is adapted to receive a pagingrequest for paging the terminal via the packet switched access. Thepaging request is for the circuit switched signaling service. Thecontrol node is adapted to determine whether a call via the internetprotocol domain and the packet switched access is or is beingestablished for the terminal depending on the received paging request.The control node is adapted to send a paging rejection for rejecting thereceived paging request depending on the call via the internet protocoldomain and the packet switched access is or is being established for theterminal and to send, via the packet switched access, a paging requestfor paging the terminal depending on the call via the internet protocoldomain and the packet switched access is not or is being not establishedfor the terminal.

According to another exemplary aspect of the invention, a terminal to beusable in association with terminating a circuit switched signalingservice to the terminal via a circuit switched access of a mobilenetwork is provided. The signaling service is different from a voicecall via the circuit switched access and from a mobile terminatinglocation request service. A call via an internet protocol domain of themobile network and a packet switched access of the mobile network is oris being established for the terminal. The terminal is adapted toreceive, via the packet switched access, a paging request for paging theterminal. The paging request is for the circuit switched signalingservice. The terminal is adapted to determine whether a call via theinternet protocol domain and the packet switched access is establishedfor the terminal depending on the received paging request. The terminalis adapted to send, via the packet switched access, a paging rejectionfor rejecting the paging request depending on the call via the internetprotocol domain and the packet switched access is or is beingestablished for the terminal and to send a paging response for acceptingthe paging request depending on the call via the internet protocoldomain and the packet switched access is not or is being not establishedfor the terminal.

According to another exemplary aspect of the invention, a terminal to beusable in association with terminating a circuit switched signalingservice to the terminal via a circuit switched access of a mobilenetwork is provided. The signaling service is different from a voicecall via the circuit switched access and from a mobile terminatinglocation request service. A call via an internet protocol domain of themobile network and a packet switched access of the mobile network is oris being established for the terminal. The terminal is adapted toreceive a paging request for paging the terminal via the packet switchedaccess. The paging request is for the circuit switched signalingservice. The terminal is adapted to determine whether a signalingservice via the internet protocol domain is available for the terminaldepending on the received paging request. The signaling service via theinternet protocol domain corresponds to the circuit switched signalingservice. The terminal is adapted to send, via the packet switchedaccess, a support indication indicating a terminal support for thesignaling service via the internet protocol domain depending on thesignaling service via the internet protocol domain being available forthe terminal.

According to another exemplary aspect of the invention, a communicationsystem for terminating a circuit switched signaling service to theterminal via a circuit switched access of a mobile network is provided.The communication system comprises at least one of a control nodedescribed above and a terminal described above.

According to another exemplary aspect of the invention, a computerprogram to be executable by at least one processor is provided. Theexecution of the computer program causes a control node to perform amethod described above.

According to another exemplary aspect of the invention, a computerprogram to be executable by at least one processor is provided. Theexecution of the computer program causes a terminal to perform a methoddescribed above.

The foregoing and other objects, features and advantages of theembodiments will become more apparent in the following detaileddescription of embodiments as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating a method to be used in associationwith terminating a circuit switched signaling service to a terminal viaa circuit switched access of a mobile network according to anembodiment.

FIG. 2 is a flow diagram illustrating a method to be used in associationwith terminating a circuit switched signaling service to a terminal viaa circuit switched access of a mobile network according to anotherembodiment.

FIG. 3 is a flow diagram illustrating exemplary signaling exchangesperformed subsequent to the method of FIG. 2.

FIG. 4 is a flow diagram illustrating a method to be used in associationwith terminating a circuit switched signaling service to a terminal viaa circuit switched access of a mobile network according to anotherembodiment.

FIG. 5 is a flow diagram illustrating a method to be used in associationwith terminating a circuit switched signaling service to a terminal viaa circuit switched access of a mobile network according to anotherembodiment.

FIG. 6 is a flow diagram illustrating a method to be used in associationwith terminating a circuit switched signaling service to a terminal viaa circuit switched access of a mobile network according to anotherembodiment.

FIG. 7 is a block diagram illustrating a control node for a mobilenetwork according to an embodiment.

FIG. 8 is a block diagram illustrating a terminal to be usable inassociation with terminating a circuit switched signaling service to theterminal via a circuit switched access of a mobile network according toan embodiment.

FIG. 9 is a block diagram illustrating a terminal to be usable inassociation with terminating a circuit switched signaling service to theterminal via a circuit switched access of a mobile network according toanother embodiment.

FIG. 10 is a flow diagram illustrating a method to be used inassociation with terminating a circuit switched signaling service to aterminal via a circuit switched access of a mobile network according toanother embodiment.

FIG. 11 is a flow diagram illustrating a method to be used inassociation with terminating a circuit switched signaling service to aterminal via a circuit switched access of a mobile network according toanother embodiment.

DETAILED DESCRIPTION

It is noted that the illustration in the drawings is schematic. Further,in different figures, identical or similar steps or elements areprovided with the same reference numerals or with reference numeralswhich are different from the corresponding reference numerals onlywithin the first digit.

In the following, methods, nodes, a terminal, a communication system,and computer programs to be used in association with terminating acircuit switched signaling service to a terminal via a circuit switchedaccess of a mobile network according to embodiments are described inmore detail.

According to embodiments, a terminal may connect or may be connected toa mobile network or cellular network by means of a call via an internetprotocol domain of the mobile network and a packet switched access themobile network. The terminal may be attached to the mobile network andthe latter mentioned call may be currently being established for theterminal or in other words the call establishment may be currently inprogress. In this respect, a bearer for the call may be established andoptionally signaling related to the call establishment may also beexchanged. Alternatively, the call may be already established,particularly for the terminal. A circuit switched signaling service isto be terminated to the terminal via a circuit switched access of themobile network. The circuit switched signaling service may be differentfrom or compared to a voice call established, currently beingestablished or to be established via the circuit switched access of themobile network and/or a mobile terminating location request signalingservice, particularly a MT-LR signaling service mentioned in thebackground section.

To this end, in a first embodiment, a control node of a packet switcheddomain of the mobile network might not send a paging request to theterminal depending on a result of a determination performed by thecontrol node and pertaining to whether the call via the internetprotocol domain is or is currently being established for the terminal ornot. In a case in which a call is established or is currently beingestablished, the control node may send a paging rejection to the networksubsequent to a received paging request instead of sending the pagingrequest to the terminal. In a second embodiment, the terminal may becapable of rejecting a received paging request, particularly by sendinga paging rejection, depending on a result of a determination performedby the terminal and pertaining to whether the call via the internetprotocol domain is or is currently being established for the terminal ornot. In a third embodiment, the terminal can initiate a termination of acorresponding signaling service via the internet protocol domain insteadof the circuit switched signaling service depending on a result of adetermination performed by the terminal and pertaining to whether such acorresponding signaling service being available or not particularly forthe terminal.

In the second and third embodiments, the terminal may additionallydetermine whether a call continuity procedure, for example Single RadioVoice Call Continuity (SRVCC), should be applied or not for the callestablished or currently being established via the internet protocoldomain. In this respect, the terminal may determine whether the callcontinuity procedure should be applied for transferring the call fromthe packet switched access to the circuit switched access. The terminalmay perform the call continuity procedure depending on a result of thedetermination. For example, SRVCC can be performed for the call being anin pre-alerting state, i.e. in a state in which a corresponding bearerfor the call is established and signaling for the call establishment hasbeen transmitted. In the pre-altering state ringing tones might not betransmitted yet. A corresponding mode of the terminal may be calledpre-alternating mode. SRVCC can also be performed for the call being inan alerting state, i.e. in a state in which the bearer for the call isestablished, but the call is not established yet. Ringing tones for thecall may be already transmitted. A corresponding mode of the terminalmay be called alerting mode. SRVCC can be also performed for anestablished call, i.e. when the call and the corresponding bearer isestablished. In this case, the call can be also in its held state, wherethe communication for the call is currently suspended.

The result of the above mentioned determinations may contribute to theabove specified action of the control node and the terminal,respectively. A further result of one or more further determinations mayalso impact the action of the control node and the terminal,respectively, to be performed. Hence, the action to be performed by therespective entity may have multiple dependencies. Hence, the action ofthe respective entity may be caused by a result of one or moredeterminations.

The inventors have beneficially recognized that measures to be used inassociation with terminating a circuit switched signaling servicedifferent from a mobile terminating location request signaling serviceduring a call of the terminal established or currently being establishedvia the internet protocol domain of the mobile network are not existingso far. The above described embodiments may therefore enable that aninterruption of the established call or the call being currentlyestablished may be omitted.

In the following, further embodiments of the method performed by thecontrol node will be described. It is noted that these embodiments maysimilarly apply to the method performed by the terminals, the controlnode, the terminals, the communication system, and/or the computerprograms.

In particular, the term “adapted” can particularly denote “embodied” inthis application.

In particular, the circuit switched signaling service may be embodied asterminating signaling service, i.e. a signaling service to be terminatedto the terminal.

In particular, as mentioned above, the term “mobile network” may denotea cellular network or a communication network, in which a communicationbetween a terminal and the network may be wireless.

In particular, the circuit switched signaling service can be networkinitiated and/or may be adapted, for example, as a non call relatedsignaling service. Such a non call related service may be asupplementary service, for example an Unstructured Supplementary ServiceData (USSD) service or an Unregistered Digital Information (UDI). UDImay be used between terminals.

The step of determining may comprise determining whether bearerinformation for the terminal may be available in the control node, thebearer information indicating that a bearer for transporting a call viathe internet protocol domain and the packet switched access may beestablished for the terminal, and the step of sending the pagingrejection may be performed depending on the bearer information for theterminal being available in the control node, wherein the step ofsending the paging request may be performed depending on the controlnode being free of the bearer information for the terminal.

The method may further comprise determining whether the control node mayhave sent a termination indication to the terminal, the terminationindication indicating that a circuit switched short messaging servicemay be terminatable to the terminal via the packet switched access,wherein the step of sending the paging rejection may be performeddepending on the control node having sent the termination indication,wherein the step of sending the paging request via the packet switchedaccess may be performed depending on the control node having not sentthe termination indication.

The method may further comprise starting a timer and a counter in thecontrol node in response to the received paging request, the timerrunning for a predetermined time interval, the counter counting a numberof paging requests received by the control node, receiving at least afurther paging request for paging the terminal via the packet switchedaccess, and sending, via the packet switched access, a further pagingrequest depending on a counted number of received paging requests beingequal to or exceeding a predetermined number of paging requests withinthe predetermined time interval.

At least one of the received paging request, the received at leastfurther paging request, the sent paging request and the sent furtherpaging request may comprise an identification of the circuit switchedsignaling service, particularly a Supplementary Service serviceIdentification.

In the following, further embodiments of the method performed by theterminal and comprising the step of determining whether a call is or iscurrently being established will be described. It is noted that theseembodiments may similarly apply to the method performed by therespective other entities, the control node, the terminals, thecommunication system, and/or the computer programs.

In particular, the paging rejection sent by the terminal may be a pagingerror for indicating an unsuccessful handling of the paging request bythe terminal.

In particular, the paging response sent by the terminal may be forindicating a successful handling of the paging request by the terminalalternatively or additionally to for accepting the paging request.

The step of determining may comprise using information provided from afirst protocol layer in the terminal, particularly an Internet ProtocolMultimedia Subsystem layer, to a lower second protocol layer in theterminal, particularly a Non Access Stratum layer.

The information may be provided from the first protocol layer uponrequest from the lower second protocol layer.

The method may further comprise at least one of determining whether theterminal may will receive the circuit switched signaling service, anddetermining whether the terminal may will perform a call continuityprocedure for the call from the packet switched access to the circuitswitched access, wherein the step of sending the paging rejection may beperformed depending on the terminal may will receive the circuitswitched signaling service and/or depending on the terminal may willperform the call continuity procedure.

The paging rejection may comprise a call continuity indicationindicating to initiate, for the call of the terminal, a call continuityprocedure from the packet switched access to the circuit switchedaccess, particularly an error code of a first type.

The method may further comprise performing the call continuity procedurefor the call of the terminal subsequent to an access node of the mobilenetwork requesting to perform the call continuity procedure.

The step of sending the paging rejection may be performed depending onthe terminal might will not receive the circuit switched signalingservice and/or depending on the terminal might will not perform the callcontinuity procedure, and/or wherein the sent paging rejection maycomprise an error indication indicating a rejection of the pagingrequest by the terminal, particularly an error code of a second type.

The method may further comprise determining whether a signaling servicevia the internet protocol domain may be available for the terminal, thesignaling service via the internet protocol domain corresponding to thecircuit switched signaling service to be terminated, and sending, viathe packet switched access, a support indication indicating a terminalsupport for the signaling service via the internet protocol domaindepending on the signaling service via the internet protocol domainbeing available for the terminal.

The method may further comprise determining whether the terminal may beregistered in the signaling service via the internet protocol domain,wherein the support indication may be sent together with a registrationrequest for registering in the signaling service via the internetprotocol domain depending on the terminal being not registered in thesignaling service via the internet protocol domain, wherein the supportindication may be sent without the registration request for registeringin the signaling service via the internet protocol domain depending onthe terminal being registered in the signaling service via the internetprotocol domain.

In the following, further embodiments of the method performed by theterminal and comprising the step of determining whether a correspondingsignaling service being available will be described. It is noted thatthese embodiments may similarly apply to the method performed by therespective other entities, the control node, the terminals, thecommunication system, and/or the computer programs.

The method may further comprise sending, via the packet switched access,a paging rejection for rejecting the paging request depending on thereceived paging request and particularly depending on a result of thestep of determining.

The method may further comprise determining whether a call via theinternet protocol domain and the packet switched access may be or may bebeing established for the terminal depending on the received pagingrequest, wherein the step of sending the paging rejection may beperformed depending on the call via the internet protocol domain and thepacket switched access may be or may be being established for theterminal.

In the following, further embodiments of the control node will bedescribed. It is noted that these embodiments may similarly apply to themethods, the terminals, the communication system, and/or the computerprograms.

The control node may be adapted to perform the method as describedabove.

In the following, further embodiments of the terminal will be described.It is noted that these embodiments may similarly apply to the methods,the control node, the respective other terminal, the communicationsystem, and/or the computer programs.

The terminal may be adapted to perform the method as described above.

Referring to FIG. 1, a method to be used in association with terminatinga circuit switched signaling service to a terminal via a circuitswitched access of a mobile network according to an embodiment will beexplained.

A respective mobile network 100 comprises a first control node 102, asecond control node 104, and an access node 106. A terminal 108 isconnectable to the mobile network 100. The first control node 102 can bepart of a circuit switched domain of a core network of the mobilenetwork 100 and can be adapted as a Mobile Switching Center (MSC). Thefirst control node 102 may further be adapted to control a payload andsignaling transmission via the circuit switched access of the mobilenetwork 100. The second control 104 can be part of a packet switcheddomain of the core network of the mobile network 100 and may be adaptedas a Mobility Management Entity (MME). The second control node 104 maybe further adapted to control a payload and signaling transmission via apacket switched access of the mobile network 100. The circuit switchedaccess and/or the packet switched access may be adapted as radio accessnetwork. The circuit switched access may be embodied as, for example, aGlobal System for Mobile Communications (GSM) Enhanced Data Rates forGSM Evolution (EDGE) Radio Access Network (GERAN) or Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access Network(UTRAN) access network, and the packet switched access may be embodiedas a Long Term Evolution (LTE) network.

The mobile network 100 further comprises an internet protocol domain,for example an Internet Protocol (IP) Multimedia Subsystem (IMS) domain.The access node 106 may be part of the packet switched access and may beadapted as an eNodeB. The terminal 108, for example a cellular phone ora tablet, is attached via the packet switched access to the secondcontrol node 104 and further to the internet protocol domain. The methodis performed by the second control node 104. Further steps in FIG. 1which are not performed by the second control node 104 are also labeledby a reference numeral for ease of explanation.

As illustrated by a first step 110, a call via the internet protocoldomain and the packet switched access is established for the terminal108, and the terminal 108 is in an active mode, i.e. the terminal 108can send data to and/or receive data from a radio access, here thepacket switched access. In its active mode, the terminal 108 can alsocurrently communicate with a peer end of the established call.Alternatively, the call via the internet domain and the packet switchedaccess may be currently being established for the terminal 108. In thelatter option, the terminal 108 may be also in its active mode. The callmay be adapted as IMS voice call, an IMS video call or an IMS Voice overInternet Protocol (VoIP) call. It is noted that the abbreviation “ps” inthe Figures denotes “packet switched” and the abbreviation “cs” in theFigures denotes “circuit switched”.

In response to a trigger message received by the first control node 102in a step 112, the first control node 102 sends in a step 114 a pagingrequest for paging the terminal 108 via the packet switched access tothe second control node 104. The paging request is associated with thecircuit switched signaling service to be terminated to the terminal 108.In this respect, the paging request may be sent via a particularinterface between the first and second control nodes 102, 104,particularly a SGs interface. The paging request may comprise acorresponding identification of the circuit switched signaling serviceto be terminated to the terminal 108 via the circuit switched access.The identification may be configured as a Supplementary Service (SS)service Identification (ID) or SS Code, for example defined inaccordance with TS 29.009 V11.0.0 (2012-09) or TS 29.002 V12.0.0(2013-03). The identification may be included in the paging request in acase in which the identification may be specified, for example in thelatter mentioned Technical Specifications. Additionally oralternatively, the identification may have to be included in the pagingrequest in a case in which a non-call related supplementary serviceshould be indicated. In a case of USSD, a recipient of the pagingrequest may recognize the kind of signaling service from the pagingrequest. The circuit switched signaling service is different from avoice call established via the circuit switched access and from a mobileterminating location request service, for example a Mobile TerminatingLocation Request (MT-LR) service as defined in TS 23.272 V11.4.0(2013-03). Further, the circuit switched signaling service can benetwork initiated and/or may be adapted, for example, as a non callrelated signaling service, for example in the form of a USSD service.

The second control node 104 receives the paging request in the step 114.The second control node 104 determines in response to the receivedpaging request in a next step 116 whether the second control node 104has previously sent a termination indication to the terminal 108particularly in response to a receipt of the termination indication fromthe terminal 108. For example, the termination indication may have beenpreviously sent during an attach procedure of the terminal 108 forattaching to the mobile network 100 or during a location updateprocedure for updating a location of the terminal both to the packetswitched access and the circuit switched access, particularly a combinedTracking Area (TA) and Location Area (LA) Update. The terminationindication indicates that a circuit switched short messaging service,for example a SMS service, is terminatable to the terminal 108 via thepacket switched access by the second control node 104, hence the secondcontrol node 104 supports the termination of the circuit switched shortmessaging service to the terminal 108 via the packet switched access.The termination indication can be adapted as “SMS only” indicationassociated with CSFB for only SMS service. Sending the terminationindication by the second control node 104 may imply that a circuitswitched short messaging service can be terminated to the terminal 108without performing the circuit switched fallback procedure, since thisparticular signaling service can also be terminated via the packetswitched access. Hence, sending a paging request from the second controlnode 104 to the terminal 108 via the packet switched access may besuperfluous. Not sending the termination indication may require theterminal 108 to perform the circuit switched fallback procedure, inorder to receive a circuit switched signaling service. Hence, a pagingrequest for the circuit switched signaling service may have to be sentfrom the second control node 104 to the terminal 108.

A determination rule associated with the determination in the step 116may set forth that the paging request is to be rejected by acorresponding paging rejection for rejecting the received paging requestin a case in which the determination is in the affirmative and that apaging request is to be sent to the terminal 108 else. The pagingrequest to be sent to the terminal 108 may be specified to be the pagingrequest received in the step 112, thereby the second control node 104forwarding the paging request received from the first control node 102to the terminal 108. It is assumed that the determination in thisembodiment is in the affirmative.

In a next step 118, the second control node 104 determines whether acall via the internet protocol domain and the packet switched access isestablished or is being established for the terminal 108 depending onthe received paging request. To this end, the second control node 104determines whether bearer information, particularly for the terminal108, is available in the second control node 104. The bearer informationindicates that a bearer for transporting a call via the internetprotocol domain and the packet switched access is established for theterminal 108. The bearer information may indicate a call via theinternet protocol domain and the packet switched access being, at leastpotentially, established for the terminal 108. In this respect, a bearermay be considered to be an information transmission context or path ofdefined characteristics, for example capacity, delay and/or bit errorrate. The bearer information may be specific for the terminal in thatthe bearer may be established for the terminal 108. For example, thebearer information can be adapted as information related to an EPSbearer particularly associated with the terminal 108, for exampleinformation related to a QCI=1 bearer which may be set up for theterminal 108. Since the bearer information may be present in the secondcontrol node 104 in a case in which the call via the internet protocoldomain may be established or the call establishment of such a call maybe still in progress, the determination in the step 118 may employ theassumption that a call via the internet protocol domain may potentiallybe established if the bearer information are present.

A determination rule associated with this determination step 118 mayspecify that the paging request may be rejected by a paging rejection tobe sent to the first control node 102 in a case in which thedetermination is in the affirmative and that a paging request may besent to the terminal 108 in a case in which the determination is not inthe affirmative. Further, the paging request to be sent to the terminal108 can be specified in the second control node 104 to be the pagingrequest received from the first control node 102, as is described above.The circuit switched signaling procedure may be terminated in accordancewith a mobile terminating call procedure, for example as described in TS23.272 V11.4.0 2013-03), clause 7. In the described embodiment, thedetermination is assumed to be in the affirmative.

The step 118 can be performed prior to the step 116.

In order to account for the two successively performed determinationsand the determination rules thereof, a combined determination rule ofthe second control node 104 may specify that the paging request isrejected by sending a paging rejection to the first control node 102 ina case in which the determination in the step 116 is in the affirmative,the determination in the step 118 is in the affirmative or thedetermination in the steps 116 and 118 are both in the affirmative. Onthe contrary, according to the combined determination rule, the pagingrequest is to be sent, particularly from the second control node 104,via the packet switched access to the terminal 108 in a case in whichthe determination in the step 116 and 118 are both not in theaffirmative. Further, the paging request to be sent may be specified tobe the paging request received from the first control 102, hence thesecond control node 104 is to forward the received paging request to theterminal 108 via the packet switched access. The forwarded pagingrequest therefore may comprise the identification of the circuitswitched signaling service to be terminated. Alternatively, the pagingrequest to be sent may be specified in the second control node 104 to bea paging request different from the received paging request. Hence thesent paging request might not comprise the identification of the circuitswitched signaling service.

Additionally or alternatively, the sent paging request and the forwardedpaging request, respectively, may be for the circuit switched signalingservice in that the terminal 108 may be capable of differentiatingbetween a paging associated with a circuit switched signaling serviceand other kind of paging purposes. In this respect, the respectivepaging request may comprise a protocol marking, for example a corenetwork domain indication indicating a circuit switched domain of themobile network such that the terminal 108 may recognize that the pagingis for a circuit switched fallback procedure. Such a core network domainindication may be embodied as a Core Network (CN) Domain indicator asspecified in TS 23.401 V12.0.0 (2013-03). Additionally or alternatively,the respective paging request may comprise parameters as specified in TS23.401 V12.0.0 (2013-03).

Additionally or alternatively, the sent paging request and the forwardedpaging request, respectively, may comprise the identification of thecircuit switched signaling service mentioned above. Additionally oralternatively, the identification may be included in the respectivepaging request in a case in which the identification may be specified,for example in the above mentioned Technical Specifications.Additionally or alternatively, the identification may have to beincluded in the respective paging request in a case in which a non-callrelated supplementary service should be indicated. In a case of USSD, arecipient of the respective paging request may recognize the kind ofsignaling service from the respective paging request. Additionally oralternatively, the respective paging request may have to comprise theidentification in a case in which the terminal 108 may be in its activemode. Therefore the terminal 108 may be informed by the respectivepaging request for which service the terminal 108 may be paged. Forexample, the terminal 108 can be informed of a short messaging service,hence SMS, a call, or a USSD service.

In a next step 120 a, the paging request is rejected by the secondcontrol node 104 by sending a paging rejection to the first control node102 depending on the previously performed determinations, particularlydepending on the result of the previously performed determinations.Further, the termination of the circuit switched signaling service maybe cancelled by the first control node 102 and a circuit switchedfallback procedure for the terminal 108 may stop. The circuit switchedfallback procedure may have been initiated by the first control node 102of the mobile network 100, for example because of the circuit switchedsignaling service being embodied as a terminating signaling service, inorder to enable the terminal 108 to receive the terminating circuitswitched signaling service via the circuit switched access. Thereuponthe method stops.

Alternatively, a paging request may be sent in a step 120 b to theterminal 108 in a case in which the determination in the steps 116 and118 are both not in the affirmative. The initiated circuit switchedfallback procedure may therefore continue.

The step 116 may be omitted in the method.

Referring to FIG. 2, a method to be used in association with terminatinga circuit switched signaling service to a terminal via a circuitswitched access of a mobile network according to another embodiment willbe explained. The mobile network 100 associated with this method issimilar to the mobile network 100 described in FIG. 1 and the circuitswitched signaling service to be terminated is identical to the circuitswitched signaling service described in FIG. 1. Communication in themobile network 100 may be adapted as a protocol layer stackedcommunication. The method is performed by the terminal 108. Furthersteps in FIG. 2 which are not performed by the terminal 108 are alsolabeled by a reference numeral for ease of explanation.

As illustrated by a first step 110, a call via the internet protocoldomain and the packet switched access is established for the terminal108, and the terminal 108 is in an active mode. Alternatively, the callvia the internet domain and the packet switched access may be currentlybeing established for the terminal 108. The call may be adapted as IMSvoice call, an IMS video call or an IMS VoIP call.

In a step 220 b, the terminal 108 receives a paging request from thesecond control node 104 via the packet switched access. The pagingrequest may be the paging request sent in the step 120 b of FIG. 1. Thepaging request is for the circuit switched signaling service to beterminated, particularly as explained with reference to the sent pagingrequest and forwarded paging request, respectively, of FIG. 1, and maycomprise an identification of the circuit switched signaling service tobe terminated to the terminal 108. In a next step 222, the terminal 108determines whether a call via the internet protocol domain and thepacket switched access is established or is currently being establishedfor the terminal 108. The determination is triggered by the receipt ofthe paging request in the step 220 b.

To this end, the terminal 108 uses terminal information about thepresence of a call which is or is currently being established via theinternet protocol domain and the packet switched access for the terminal108. The information may be instantaneously provided by a first protocollayer of the stacked protocol layers in the terminal 108 to a lowersecond protocol layer of the stacked protocol layers in the terminal108. The first protocol layer may be associated with the communicationvia the internet protocol domain and may be adapted, for example, as anIMS layer. The second protocol layer may be associated with thecommunication between the packet switched access and the packet switcheddomain of the core network, respectively, and the terminal 108 and maybe adapted as a Non Access Stratum (NAS) layer. Alternatively, theinformation may be requested by the second protocol layer from the firstprotocol layer upon receipt of the paging request. The first protocollayer then provides the requested information to the second protocollayer.

The first protocol layer of the terminal 108 may beneficially be capableof determining whether a call is established or is currently beingestablished irrespectively of a default radio bearer or a dedicatedradio bearer being used for potentially transporting the audio data ofthe respective call. In this respect, the terminal 108 may use trafficflow templates defined in the terminal 108 to map the traffic flow tothe default radio bearer or to the dedicated radio bearer. The radiobearer may run from the terminal 108 towards an access node of themobile network where a bearer towards the second control node maycommence. Further, the first protocol layer of the terminal 108 may beaware of a present call being in a pre-altering state or alerting stateas corresponding signaling have already been exchanged via the firstprotocol layer. Therefore, the method described in FIG. 2 can bebeneficially combined with the method described in FIG. 1 in the case ofa default bearer being established via the second control node 104 andleading to the determination of the step 118 being not in theaffirmative.

A determination rule in the terminal 108 associated with thedetermination in the step 222 may specify that the paging request may berejected by sending a paging rejection to the second control node 104via the packet switched access in a case in which the determination isin the affirmative and that a paging response for indicating to continuewith the termination of the circuit switched signaling service may besent to the second control node 104 in a case in which the determinationis not in the affirmative. Thus, the second control node 104 may beinformed in the first mentioned case that the paging request wasreceived and handled by the terminal 108, but was rejected by theterminal 108. In the second case, the terminal 108 may accept the pagingrequest from the second control node 104 by sending the paging response.The paging rejection may comprise a call continuity indication or anerror indication. The call continuity indication indicates to initiate,for the call of the terminal 108, a call continuity procedure from thepacket switched access to the circuit switched access, particularlySingle Radio Voice Call Continuity (SRVCC). In this respect, the term“call continuity procedure from the packet switched access to thecircuit switched access” may particularly denote a procedure with whicha call may be continued via the circuit switched access by transferringthe call from the packet switched access to the circuit switched access.Further, the call continuity indication may comprise or may beconfigured as an error code of a first type. The error indication mayindicate to the mobile network 100 that the paging request was receivedby the terminal 108 but not accepted and hence rejected by the terminal108 and that the call continuity procedure might not to be initiated bythe mobile network 100. The error indication may comprise or may beconfigured as an error code of a second type. The terminal 108 maydetermine whether to include the call continuity indication or the errorindication into the paging rejection using local information in theterminal 108. The local information may comprise, for example amongstother, the information explained below with reference to subsequentsteps 224, 226. In the described embodiment, the determination isassumed to be in the affirmative.

In a next step 224, the terminal 108 determines whether the terminal 108will or voluntarily would like to receive the circuit switched signalingservice, for example in terms of the terminal 108 giving the circuitswitched signaling service precedence over other services and/or a call.In other words, the terminal 108 may determine whether the terminal 108may want to receive the circuit switched signaling service. Acorresponding determination rule in the terminal 108 may specify thatthe terminal 108 may send the paging rejection comprising the abovedescribed call continuity indication in a case in which thedetermination is in the affirmative and may send the paging rejectioncomprising the above described error indication in a case in which thedetermination is not in the affirmative. The determination is assumed tobe in the affirmative in this embodiment.

In a or the next step 226, the terminal 108 may determine whether theterminal 108 will or voluntarily would like to perform a call continuityprocedure for the call, for example in terms of the terminal 108 givingthe performance of the call continuity procedure precedence over notperforming the call continuity procedure and/or not acting in thisrespect. In other words, the terminal 108 may determine whether theterminal 108 may want to perform the call continuity procedure. Acorresponding determination rule in the terminal 108 may specify thatthe terminal 108 may send the paging rejection comprising the abovedescribed call continuity indication in a case in which thedetermination is in the affirmative and may send the paging rejectioncomprising the above described error indication in a case in which thedetermination is not in the affirmative. In the described embodiment,the determination is in the affirmative.

Information about capabilities of the terminal 108, user specificsettings in the terminal 108 and/or user input which may be input intothe terminal 108 may be used for the determinations in the steps 224and/or 226.

In a next step 228 a, the terminal 108 sends the paging rejection to thesecond control node 104, in which paging rejection the terminal 108 haspreviously included the call continuity indication prior to the sendingof the paging rejection.

In a case in which the determination in the step 222 is not in theaffirmative, the terminal 108 may send a paging response to the secondcontrol node 104 in a step 228 b.

The step 224 and/or the step 226 may be omitted in the method.

In a case in which the termination in the step 222 may be in theaffirmative and/or in which one or more of the determinations in thesteps 224, 226 may be not in the affirmative, the terminal 108 may sendthe paging rejection in the step 228 a in which the terminal 108 mayhave included the error indication.

Further, subsequent to the step 226 and prior to the steps 228 a, 228 b,the terminal 108 may determine, for example based on the identificationof the circuit switched signaling service included in the receivedpaging request, in an optional step 230 whether a signaling service viathe internet protocol domain is available for the terminal 108. Thesignaling service via the internet protocol domain corresponds to thecircuit switched signaling service to be terminated in terms of offeringa similar or identical service to the terminal 108. In this respect, thecorresponding signaling service may offer the same, less or morefunctionality compared to the circuit switched signaling service. Thecorresponding signaling service may offer a similar functionality to theterminal 108. A corresponding determination rule to be used in the step230 specifies that the terminal 108 may send a support indication to thesecond control node 104 via the packet switched access in a case inwhich the signaling service in question is available and else omit tosend a support indication. The step of sending the support indication isindicated in FIG. 2 by a reference numeral 232. The step 232 can beperformed prior or subsequent to the step 228 a, 228 b. The step 232 canalso be performed simultaneously to the step 228 a.

Assuming the determination of the step 230 to be in the affirmative, theterminal 108 may then further determine in an optional next step 234whether the terminal 108 has already registered in the correspondingsignaling service via the internet protocol domain before the sending ofthe support indication. The step 234 may only be performed if thedetermination in the step 230 is in the affirmative. Alternatively, thestep 234 may be performed irrespectively of a result of thedetermination in the step 230. A corresponding determination rule in theterminal 108 associated with the step 234 may specify that the terminal108 may send, via the packet switched access, the support indication inthe step 232 together with a registration request for registering theterminal 108 in the corresponding signaling service, if the terminal 108has not registered in the corresponding signaling service and may elsesend the support indication without an additional registration requestin the step 232. For example, in the first case the support indicationcan be included in the registration request.

In a case in which the optional steps 230, 234 are performed the pagingrejection sent in the step 228 a may comprise the error indication orthe call continuity indication depending on a pre-configuration in theterminal 108. Such a pre-configuration may overrule a result of thedeterminations in the steps 222, 224, 226 and/or correspondinglytriggered actions.

Assuming the determinations in the steps 230, 234 to be in theaffirmative, the corresponding signaling service may be terminated, forexample by the mobile network 100, via the packet switched access andthe circuit switched fallback procedure for the terminal 108 may beterminated. Further, in such a case, the paging rejection may includethe error indication.

Assuming at least one of the determinations in the steps 230, 234 to benot in the affirmative, the circuit switched signaling service may beterminated to the terminal 108. In such a case, the call continuityprocedure may be performed or might be not performed. The respectivepaging rejection may comprise the appropriate indication, i.e. the callcontinuity indication or the error indication.

A sequence of the steps 222, 224, 226, 230, 234 may be different fromthe described embodiment. For example, the steps 222, 224, 226 can beperformed in an arbitrary sequence compared to the described embodiment.The steps 230 and 234 may be performed prior to any one of the steps222, 224, 226.

Referring to FIG. 3, exemplary signaling exchanges following the methodof FIG. 2 will be explained in the following.

In a first configuration illustrated in an upper portion of FIG. 3, itis assumed that the paging rejection is sent in the step 228 a from theterminal 108 to the second control node 104 via the packet switchedaccess. The paging rejection comprises the call continuity indication.Subsequent to a receipt of the paging rejection the second control node104 sends in a step 336 a further paging rejection to the first controlnode 102 and in a step 338 a request to the access node 106 to initiatethe call continuity procedure for the internet protocol domain basedcall of the terminal 108. Accordingly, the first control node 102 may beinformed to continue the applicable circuit switched procedure in thecircuit switched access. The access node 106 initiates in a step 340,triggered by the received paging request, the call continuity procedurefor the call of the terminal 108. The terminal 108 accordinglyparticipates in the performance of the call continuity procedure,particularly for the call, in the step 340. In accordance with asuccessful call continuity procedure, the call via the internet protocoldomain is transferred from the packet switched access to the circuitswitched access. The termination of the circuit switched signalingservice to the terminal 108 is then continued to the terminal 108 viathe circuit switched access via which access the terminal 108 is thenattached to the mobile network 100 and may communicate with a peer end.Hence, the circuit switched fallback procedure may be performed alongwith the call continuity procedure. For example, the second control node104 may continue with step 3 of clause 8.3.2.2 of TS 23.272 V11.4.0(2013-03).

In this configuration, the first control node 102 may be equally usedfor the call continuity procedure and the circuit switched fallbackprocedure.

In a second configuration illustrated in a middle portion of FIG. 3, thepaging rejection including the error indication is sent from theterminal 108 to the second control node 104 in the step 228 a. Thesecond control node 104 sends in a subsequent step 336 a pagingrejection to the first control node 102 in response to a receipt of thepaging rejection including the error indication. Accordingly, the firstcontrol node 102 is informed about the rejection of the paging requestof the terminal 108, and the first control node 102 cancels thetermination of the circuit switched signaling procedure for the terminal108 and may also cancel the circuit switched fallback procedure. Thecall continuity procedure is therefore not performed for the establishedor currently being established call of the terminal 108. For example,the second control node 104 might not continue with step 3 of clause8.3.2.2 of TS 23.272 V11.4.0 (2013-03) and may only inform the firstcontrol node 102 about the paging rejection.

In a third configuration illustrated in a lower portion of FIG. 3, theterminal 108 sends the paging response to the second control node 104 inthe step 228 b. The second control node 104 sends in a subsequent step342 a corresponding paging response to the first control node 102 inresponse to a receipt of the paging response in the step 228 b.Thereupon, the termination of the circuit switched signaling service viathe circuit switched access continues in a step 346. To this end, theterminal 108 performs a circuit switched fallback procedure from thepacket switched access to the circuit switched access of the mobilenetwork 100, particularly CSFB mentioned above. For example, the firstcontrol node 102 may, upon receiving the paging response, continue withcircuit switched applicable procedures, for example for supplementaryservices as specified in TS 23.090 V11.0.0 (2012-09).

Referring to FIG. 4, a method to be used in association with terminatinga circuit switched signaling service to a terminal 108 via a circuitswitched access of a mobile network 100 according to another embodimentwill be explained. The mobile network 100 associated with the method issimilar to the mobile network 100 described with reference to FIG. 2 andthe circuit switched signaling service to be terminated is identical tothe circuit switched signaling service described in FIG. 1. The methodis performed by the terminal 108. Further steps in FIG. 4 which are notperformed by the terminal 108 are also labeled by a reference numeralfor ease of explanation.

As illustrated by a step 110, a call via an internet protocol domain ofthe mobile network 100 and the packet switched access of the mobilenetwork 100 is established for the terminal 108, and the terminal 108 isin an active mode. Alternatively, the call via the internet domain andthe packet switched access may be currently being established for theterminal 108. The call may be adapted as IMS voice call, an IMS videocall or an IMS VoIP call.

In a step 220 b, the terminal 108 receives, via the packet switchedaccess of the mobile network 100 and from the second control node 104, apaging request for paging the terminal 108. The terminal 108 thenperforms a step 230 and optionally a step 234 (not shown) both beingexplained with reference to FIG. 2. Thereupon the terminal 108 sends ina step 232 the support indication to the second control node 104, sincea corresponding signaling service via the internet protocol domain isavailable in the described embodiment. In a case in which thedetermination in the step 234 is performed, the support indication iseither sent alone or is sent together with the registration requestdepending on a result of the step 234 as explained with reference toFIG. 2. The termination of the circuit switched signaling service may bethen cancelled by the first control node 104 which has been accordinglyinformed by the second control node 104. Further, the correspondingsignaling service via the internet protocol domain may be terminated tothe terminal 108, particularly via the packet switched access. Aninitiated circuit switched fallback procedure for the terminal 108 maybe accordingly cancelled. The method then stops.

Optionally, the terminal 108 may send a paging rejection in a step 228 asimultaneously to, subsequent to or before the step 232 in which thesupport indication is sent, which paging rejection comprises a callcontinuity indication or an error indication. The terminal 106 mayinclude the respective call continuity indication or error indicationdepending on a preconfiguration in the terminal 108. Accordingly, theterminal 108 may perform the call continuity procedure or might notperform the call continuity procedure. Thereupon, the second controlnode 104 may send the paging rejection in an optional step 336 to thefirst control node 102.

The terminal 108 may also determine in an optional step 222 whether acall via the internet protocol domain is established for the terminal108. This step 222 may be optionally performed prior to the step 230 andoptionally the step 234, subsequent to the step 230 and optionally thestep 234 and prior to the step 232, or subsequent to the step 232 andprior to the step 228 a. The determination may be performed similarly asdescribed in FIG. 2. In such a case the communication in the mobilenetwork 100 may employ a stack of protocol layers. The terminal 108 mayinclude the call continuity indication or the error indication into thepaging rejection to be sent to the second control node 104 depending ona result of the determination in the step 222, as is described in FIG.2.

The terminal 108 may also perform steps 224, 226 described in FIG. 2,for example prior or subsequent to at least one of the steps 230, 222.The terminal 108 may include the call continuity indication or the errorindication into the paging rejection to be sent to the second controlnode 104 depending on a result of the determination in the step 222, asis described in FIG. 2.

Referring to FIG. 5, a method to be used in association with terminatinga circuit switched signaling service to a terminal 108 via a circuitswitched access of a mobile network 100 according to another embodimentwill be explained. The mobile network 100 associated with the method issimilar to the mobile network 100 described in FIG. 1, and the circuitswitched signaling service to be terminated is identical to the circuitswitched signaling service described in FIG. 1. The method is performedby the second control node 104.

As illustrated by a step 110, a call via an internet protocol domain ofthe mobile network 100 and the packet switched access of the mobilenetwork 100 is established for the terminal 108, and the terminal 108 isin an active mode. Alternatively, the call via the internet domain andthe packet switched access may be currently being established for theterminal 108. The call may be adapted as an IMS voice call, an IMS videocall or an IMS VoIP call.

In response to a receipt of a paging request from the first control node102 for paging the terminal 108 via the packet switched access in a step112, the second control node 104 starts a counter and a timer in thesecond control node 104 in a step 548. The timer runs for a timeinterval predetermined in the second control node 104. The countercounts a number of paging requests for paging the terminal 108 via thepacket switched access, which paging requests are received by the secondcontrol node 104. The paging requests may be for the same or for adifferent circuit switched signaling service to be terminated to theterminal 108.

Thereupon steps 116, 118 explained with reference to FIG. 1 andindicated in FIG. 5 by a circle may be performed. It is assumed thatboth determinations are in the affirmative. Further, the second controlnode 104 may then determine in a subsequent step 550 a whether a countednumber of paging requests received by the second control node 104 may beequal or may exceed a predetermined number of paging requests within thepreconfigured time interval. To this end, the second control node 104may count the number of paging requests received for the terminal 108 sofar since the timer has started and the second control node 104 maycompare the counted number of paging requests with the predeterminednumber. The predetermined number may be preconfigured in the secondcontrol node 104 and may be equal to nine. Since only one paging requesthas been received since the performance of the step 548, thedetermination is not in the affirmative.

The second control node 104 then sends in a step 120 a a pagingrejection to the first control node 102 based on the result of thedeterminations in the steps 116, 118, 550 a. In a case in which one orboth of the determinations in the steps 116, 118 is not in theaffirmative and/or the determination in the step 550 a is in theaffirmative, the second control node 104 may send a paging request tothe terminal 108 as described in FIG. 1.

A further paging request may be received by the second control node 104in a subsequent step 512 a. Further, steps 516 a, 518 b which aresimilar to the steps 116, 118 and are indicated by a further circle maybe performed by the second control node 104. Determinations in thesesteps 516 a, 518 a are assumed to be also in the affirmative in thisembodiment. Thereupon a step 550 b which is similar to the step 550 a isperformed. The determination of the latter step 550 b is not in theaffirmative. Thereupon, in a next step 520 a, the second control node104 sends in accordance with the result of the determinations in thesteps 516 a, 518 a, 550 b a paging rejection to the first control node102. In a case in which one of the determinations in the steps 516 a,518 a is not in the affirmative and/or the determination in the step 550b is in the affirmative, the second control node 104 may send a pagingrequest to the terminal 108 as described in FIG. 1.

Further six paging requests for paging the terminal 108 are received bythe second control node 104 from the first control node 102. These sixpaging requests are for a circuit switched signaling service which isdifferent from the signaling service with which the paging requestsreceived in the steps 112, 512 a are associated. The steps 516 a, 518 a,550 b described above are performed for each paging request and each ofthese paging requests is accordingly rejected by a respective pagingrejection message. The performed steps associated with the further sixpaging requests are omitted in FIG. 5 for ease of illustration.

In a next step 512 b, an eights further paging request is received bythe second control node 104 from the first control node 102. The pagingrequest is for the same circuit switched signaling service as the pagingrequest of the step 112 was for. After performing the steps 516 b, 518 bfor the eights further paging request indicated in FIG. 5 by a circleand explained above, the second control node 104 performs a step 550 cfor the received further paging request and determines that the countedtotal number of received paging requests, i.e. nine, is equal to thethreshold value of nine. In this respect, the predetermined number mayrepresent the threshold value for the determination. The second controlnode 104 may then stop the timer before an expiration of thepredetermined time interval and may also stop and optionally reset thecounter to zero. The second control node 104 sends in a step 520 b apaging request to the terminal 108 via the packet switched accessirrespectively of a result of the determinations in the steps 516 b, 518b. Accordingly, the result of the determination in the step 550 c mayoverrule the result of the determination in the steps 516 b, 518 b. Thesent paging request may be different from or may be the paging requestreceived in the step 512 b to the terminal 108, i.e. the received ninthpaging request is forwarded to the terminal 108, as is explained withreference to the sent and forwarded paging request, respectively,described in FIG. 1. Further, as explained with reference to FIGS. 1 and2, the respective paging request may comprise the identification of thecircuit switched signaling service to be terminated and/or the corenetwork domain indication. Hence, embodiments of the sent and forwardedpaging request, respectively, described with reference to FIGS. 1 and 2may also apply to the paging request of the step 520 b.

In a case in which the determination in the step 550 c might be not inthe affirmative, the second control node 104 may send a further pagingrejection to the first control 104.

The method may then stop. Alternatively, the method may proceed asdescribed in FIGS. 2, 3 or FIG. 4 and the terminal 108 may accordinglyperform the respective above explained steps. Here, the paging request520 a may correspond to the paging request sent in the step 220 a.Thereupon the method may stop.

The paging request received in the step 112 may or may not be counted bythe counter in the step 550 a. The steps 116, 118, 516 a, 516 b, 518 aand/or 518 b can be omitted in the method. The steps 550 a, 550 b, 550 ccan be performed prior to the respective steps 116 and/or 118, 516 aand/or 518 a, and 516 b and/or 518 b, respectively.

Referring to FIG. 6, a method to be used in association with terminatinga circuit switched signaling service to a terminal 108 via a circuitswitched access of a mobile network 600 according to another embodimentwill be explained. The mobile network 600 associated with the methodcomprises a first control node 602 configured as a MSC co-located with aVisitor Location Register (VLR) of a circuit switched domain of a corenetwork of the mobile network 600, and a second control node 604configured as a MME. The MME 604 is part of a packet switched domain ofa or the core network, which domain is configured as Evolved Packet Core(EPC). An internet protocol domain of the mobile network 600 isconfigured as an IMS domain. The mobile network 600 further comprises apacket switched access configured, for example as a LTE network. Acircuit switched access of the mobile network 600 can be UTRAN or GERAN.The method is performed by the MME 104 and/or the terminal 102. Furthersteps in FIG. 6 which are not performed by the latter entities are alsolabeled by a reference numeral for ease of explanation.

An IMS voice call, an IMS video call or an IMS VoIP call is establishedfor the terminal 108 via the IMS domain and the LTE access, as indicatedin a step 110. Alternatively, the call via the internet domain and thepacket switched access may be currently being established for theterminal 108. For example, the MME 604 has an established S1 connectionfor the IMS VoIP session or IMS VoIP call. In the following, theembodiment will be explained with reference to the IMS voice call andIMS video call without loss of generality.

The MSC/VLR 602 receives in a step 112 a trigger for terminating anetwork initiated circuit switched signalling service to the terminal108. The network initiated signalling service may be configured asNetwork (NW)-initiated signalling service defined for example in TS23.271 V11.3.0 (2112-12), clause 8.4.2 or TS 23.271 V11.4.0 (2113-03),clause 8.4.2.

In a next step 114, the MSC/VLR 602 sends a paging request for pagingthe terminal 108 via the packet switched access by sending a pagingmessage to the MME 604 over a SGs interface. The paging request maycomprise an identification of the circuit switched signalling service.The identification may be embodied as a SS service ID. For a callindependent supplementary service, the paging request message mustinclude the SS service ID associated with the circuit switchedsignalling service to be terminated to the terminal 108. A SS service IDfor USSD could be accordingly defined.

In a first variant of the method, the MME 604 may perform steps 116, 118explained above. A corresponding termination indication is configured as“SMS only” indication indicating support of terminating only a circuitswitched SMS service to the terminal 108 via the packet switched access.The bearer information is configured as information related to anavailability or existence of a QCI=1 bearer, particularly for theterminal 108, in the MME 604. The bearer may run via the MME 604 to anode of the packet switched access, for example an eNodeB. A radiobearer may run from the node of the packet switched access to theterminal 108.

If the MME 604 did not send the termination indication to the terminal108 by returning the “SMS-only” indication to the terminal 108 duringpreviously performed Attach or Combined Tracking Area (TA)/Location Area(LA) Update procedures, and if there is no bearer information availablein the MME 604 for the terminal 108, namely the information pertainingto the availability of a QCI=1 bearer, the MME 604 then sends in afurther step 120 b a paging request for paging the terminal 108 to theterminal 108. To this end, the MME 604 may forward the paging requestmessage received in the step 114. The sent paging request message maycomprise parameters as specified in TS 23.401 V12.0.0 (2013-03), forexample a Core Network (CN) Domain Indicator. For a call independentsupplementary service the paging request message may include the SSservice ID. The SS service ID is used to indicate the type of thesupplementary service, for example USSD, to the terminal 108. The SSservice ID must be included in the sent circuit switched paging message,if the terminal 108 is in an active mode, for example the terminal 108is currently communicating with a peer end.

An access node of the packet switched access, for example an eNodeB, mayforward the paging request to the terminal 108. This access node may bethe above mentioned access node at which the bearer from the corenetwork may terminate and from which the radio bearer towards theterminal 108 may commence.

If the MME 604 returned the “SMS-only” indication to the terminal 108during the Attach or Combined TA/LA Update procedures, or if there isthe information about the QCI=1 bearer for the terminal 108 available inthe MME 604, the MME 604 will not send the paging request message to theterminal 108, and the MME 604 sends a or the paging rejection for thecircuit switched paging request towards the MSC 602 to stop the circuitswitched paging procedure and this Circuit Switched Fallback (CSFB)procedure stops as explained in FIG. 1. The method then stops.

In a second variant of the method, the terminal 102 may perform the step222 explained in FIG. 2 subsequent to a receipt of the paging request inthe step 120 b. The second variant may represent an alternative to thefirst variant. Hence, the determination in the step 222 pertaining towhether the terminal 108 is engaged in an IMS voice call or an IMS videocall may be performed alternatively to the above described method flowcomprising the determination of the step 118 pertaining to whether thereis bearer information available in the MME 602 for the terminal 108. Thefirst variant of the method can also be combined with the second variantof the method in that the paging request message sent by the MME 604 toterminal 108 may trigger the performance of the second variant of themethod, for example in a case in which a default bearer is establishedvia the MME 604 for the IMS voice call or IMS video call instead of thededicated bearer with QCI=1.

If the terminal 108 is not engaged in an IMS voice or IMS video call,i.e. the terminal 108 is not in an active or alerting phase or mode, themobile terminating call procedure then takes place in a step 652 asspecified, for example, in clause 7 “Mobile Terminating Call Procedure”of TS 23.272 V11.4.0 (2013-03).

In the step 222, a first protocol IMS layer in the terminal 108 may needeither to inform a lower protocol NAS layer in the terminal 108 that anIMS voice call or IMS video call is on-going or is currently to beestablished or the NAS layer in the terminal 108, when receiving thepaging request message in the step 120 b, may need to request theinformation from the IMS layer in the terminal 108 by querying the IMSlayer in the terminal 108.

If the terminal 108 is engaged in an IMS voice call or IMS video call orthe establishment thereof, the terminal 108 may then perform (the) steps224 and/or 226, particularly explained with reference to FIG. 2, and maythen decide to reject the paging request message with a call continuityindication explained above and configured as an error code of a firsttype. Accordingly, in a next step, the terminal 108 sends a pagingrejection message including the error code of the first type to the MME604 such that the MME 604 is informed and continues with a step 3 asdescribed in clause 8.3.2.2 of TS 23.272 V11.4.0 (2013-03). ThereforeSRVCC is initiated and the MSC 602 is informed to continue theapplicable circuit switched procedure in a circuit switched access, forexample GERAN or UTRAN. It is noted that the latter may imply that thesame MSC 602 is used for SRVCC and for CSFB.

If the determination in the step 224 and/or 226 is not in theaffirmative, for example if the terminal 108 does not want to performSRVCC and/or to receive the NW-initiated circuit switched service, thenthe terminal 108 rejects the paging request message by sending, to theMME 604, a paging rejection including an error indication which isexplained above and which is configured as an error code of a secondtype. Accordingly, the MME 604 does not continue with step 3 asdescribed in clause 8.3.2.2 of TS 23.272 V11.4.0 (2013-03), and insteadonly informs the MSC 602 about the paging rejection by sending arespective paging rejection message.

In a third variant of the method, the terminal 108 may perform the step230 and optionally the step 234 particularly explained above. The thirdvariant may represent an alternative to both the first and secondvariant of the method or may follow the procedures of the first and/orsecond variant of the method. Steps of the third variant may also bepart of the second variant, as explained with reference to FIG. 2. Thepaging request received by the terminal 108 may comprise a SS serviceID.

Accordingly, if the terminal 108 receives a paging message with an SSservice ID for which an IMS service is also available, for examplesupport of terminating IMS USSD, and the terminal 108 has not registeredyet for that IMS service, the terminal 108 may then perform an IMSregistration using an or the associated registration request messagecomprising a support indication indicating support for this IMS service,as explained above particularly with reference to steps 230, 234 and232. The mobile network 600 should then use the IMS service instead ofthe circuit switched service for termination.

The first variant of the method may be combined with the second and/orthird variant of the method by the MME 604 employing a timer and acounter. Respective steps 548, 550 a, 550 b, 550 c explained above maybe performed by the MME 604 prior to sending a, for example forwardingthe, further paging request to the terminal 108. A respective rule inthe MME 604 associated with the timer and the counter may specify thefollowing: If within a predetermined time interval a predeterminednumber of terminating NW-initiated circuit switched signalling servicerequests is counted by the counter, the paging request is then sent tothe terminal 108 and the second and/or third variant of the methodcontinues. The predetermined number of the terminating NW-initiatedcircuit switched service requests may be compared to the counted numberof paging requests in the steps 550 a, 550 b, 550 c.

The terminal 102 may also send a paging response message to the MME 604in a step 228 b which in turn sends a paging response to the MSC 602 ina step 342 in a case in which the determination of the terminal 108 inthe step 222 is not in the affirmative, hence the terminal 108 is notengaged in an IMS voice call or IMS video call.

Once the paging response is successfully returned to the MSC 602 in thestep 342, the applicable circuit switched procedures continues,particularly in the step 346, for example for a supplementary service asspecified in specifications such as TS 23.090 V11.0.0 (2012-09).

Referring to FIG. 7, a control node 704 for a mobile network accordingto an embodiment will be described. The control node 704 can be thecontrol node 104 or the control node 604 and can be the MME described inthe following FIGS. 10 and 11. The control node 704 is usable inassociation with terminating a circuit switched signaling service to aterminal via a circuit switched access of a mobile network. Thesignaling service is different from a voice call via the circuitswitched access and from a mobile terminating location request service.A call via an internet protocol domain of the mobile network and apacket switched access of the mobile network is or is being establishedfor the terminal. The control node 704 is adapted to receive a pagingrequest for paging the terminal via the packet switched access, thepaging request being for the circuit switched signaling service. Thecontrol node 704 is further adapted to determine whether a call via theinternet protocol domain and the packet switched access is or is beingestablished for the terminal depending on the received paging request,and to send a paging rejection for rejecting the received paging requestdepending on the call via the internet protocol domain and the packetswitched access is or is being established for the terminal and to send,via the packet switched access, a paging request for paging the terminaldepending on the call via the internet protocol domain and the packetswitched access is not or is being not established for the terminal. Thecontrol node 704 can be adapted to perform the method described aboveand/or below.

The control node 704 may comprise one or more processors 760 adapted toperform the above functionalities of the control node 704. The controlnode 704 may further comprise an interface 762 to which the one or moreprocessors 760 are coupled and via which the paging request can bereceived and/or via which the paging rejection, the paging requestand/or the paging response described above can be sent. The control node704 may further comprise a memory 764 coupled to the one or moreprocessors 760. The memory 764 may include a ROM, for example, a flashROM, a RAM, e.g., a DRAM or SRAM, a mass storage, for example, a harddisk or solid state disk, or the like. The memory 764 may includesuitably configured program code, particularly embodied as one or moremodules, to be executed by the one or more processors 760 so as toimplement the above-described functionalities of the control node 704.In particular, the memory 764 may comprise a determination module 766implementing the above described determination functionalities of thecontrol node 704. The determination module 766 may also implement thefunctionality of the control node 704 relating to the receiving of apaging request. Alternatively or additionally, the memory 764 maycomprise a receiving module 767 implementing the latter describedreceiving functionality. The determination module 766 may also implementthe functionality of the control node 704 relating to the sending of apaging rejection, a paging request and/or a paging response.Alternatively or additionally, the memory 764 may comprise a sendingmodule 768 implementing the latter described sending functionality.Further, the memory 764 may also comprise a control module 770 forimplementing various control functionalities of the control node 704,for example for controlling the payload and signaling transmission viathe packet switched access.

It is to be understood that the structures as illustrated in FIG. 7 aremerely schematic and that the control node 704 may actually includefurther components which, for the sake of clarity, have not beenillustrated, for example, further interfaces or processors. Also, it isto be understood that the memory 764 may include further types ofprogram code modules, which have not been illustrated, for example,program code modules for implementing known functionalities of a MME.According to some embodiments, a computer program may be provided. Thecomputer program may be embodied as or may comprise the above programcode. The computer program may be executable by the one or moreprocessors 760 of the control node 704. The execution of the computerprogram by the one or more processors 760 may cause the control node 704to perform a method described above and/or below. According to someembodiments, also a computer program product may be provided forimplementing functionalities of the control node 704, for example, inthe form of a medium storing the program code and/or other data to bestored in the memory 764.

Referring to FIG. 8, a terminal 808 to be usable in association withterminating a circuit switched signaling service to the terminal 808 viaa circuit switched access of a mobile network according to an embodimentwill be described. The terminal 808 may be embodied as the terminal 108described above or as the terminal described in the following FIGS. 10and 11. The signaling service is different from a voice call via thecircuit switched access and from a mobile terminating location requestservice. A call via an internet protocol domain of the mobile networkand a packet switched access of the mobile network is or is beingestablished for the terminal 808. The terminal 808 is adapted toreceive, via the packet switched access, a paging request for paging theterminal 808. The paging request is for the circuit switched signalingservice. The terminal 808 is further adapted to determine whether a callvia the internet protocol domain and the packet switched access is or isbeing established for the terminal 808 depending on the received pagingrequest, and to send, via the packet switched access, a paging rejectionfor rejecting the paging request by the terminal 808 depending on thecall via the internet protocol domain and the packet switched access isor is being established for the terminal 108 and to send a pagingresponse for accepting the paging request by the terminal 108 dependingon the call via the internet protocol domain and the packet switchedaccess is not or is being not established for the terminal 808. Theterminal 808 may be adapted to perform the method as described aboveand/or below.

The terminal 808 may comprise one or more processors 860 adapted toperform the above functionalities of the terminal 808. The terminal 808may further comprise an interface 862 to which the one or moreprocessors 860 are coupled and via which the paging request can bereceived and/or via which the paging rejection, the paging response, thesupport indication and/or the registration request described above canbe sent. The terminal 808 may further comprise a memory 864 coupled tothe one or more processors 860. The memory 864 may include a ROM, forexample, a flash ROM, a RAM, e.g., a DRAM or SRAM, a mass storage, forexample, a hard disk or solid state disk, or the like. The memory 864may include suitably configured program code, particularly embodied asone or more modules, to be executed by the one or more processors 860 soas to implement the above-described functionalities of the terminal 808.In particular, the memory 864 may comprise a determination module 866implementing the above described determination functionalities of theterminal 808. The determination module 866 may also implement thefunctionality of the terminal 808 relating to the receiving of a pagingrequest. Alternatively or additionally, the memory 864 may comprise areceiving module 867 implementing the latter described receivingfunctionality. The determination module 866 may also implement thefunctionality of the terminal 808 relating to the sending of a pagingrejection in which the call continuity indication or the errorindication may be included, a paging response, a support indicationand/or the registration request. Alternatively or additionally, thememory 864 may comprise a sending module 868 implementing the latterdescribed sending functionality. Further, the memory 864 may alsocomprise a control module 870 for implementing various controlfunctionalities of the terminal 808, for example for controllingoperations related to sending feedback messages or receiving controlmessages via the interface 862.

Referring to FIG. 9, a terminal 908 to be usable in association withterminating a circuit switched signaling service to the terminal 908 viaa circuit switched access of a mobile network according to anotherembodiment is described. The terminal 908 may be embodied as theterminal 108 described above or as the terminal described in thefollowing FIGS. 10 and 11. The signaling service is different from avoice call via the circuit switched access and from a mobile terminatinglocation request service. A call via an internet protocol domain of themobile network and a packet switched access of the mobile network is oris being established for the terminal 908. The terminal 908 is adaptedto receive a paging request for paging the terminal 908 via the packetswitched access. The paging request is for the circuit switchedsignaling service. The terminal 908 is adapted to determine whether asignaling service via the internet protocol domain is available for theterminal 908 depending on the received paging request. The signalingservice via the internet protocol domain corresponds to the circuitswitched signaling service. The terminal 908 is further adapted to send,via the packet switched access, a support indication indicating aterminal support of or for the signaling service via the internetprotocol domain depending on the signaling service via the internetprotocol domain being available for the terminal 908. The terminal 908may be also adapted to perform a method as described above and/or below.

The terminal 908 may comprise one or more processors 960 adapted toperform the above functionalities of the terminal 908. The terminal 908may further comprise an interface 962 to which the one or moreprocessors 960 are coupled and via which the paging request can bereceived and/or via which the support indication, a paging rejection, apaging response and/or a registration request described above can besent. The terminal 908 may further comprise a memory 964 coupled to theone or more processors 960. The memory 964 may include a ROM, forexample, a flash ROM, a RAM, e.g., a DRAM or SRAM, a mass storage, forexample, a hard disk or solid state disk, or the like. The memory 964may include suitably configured program code, particularly embodied asone or more modules, to be executed by the one or more processors 960 soas to implement the above-described functionalities of the terminal 908.In particular, the memory 964 may comprise a determination module 966implementing the above described determination functionalities of theterminal 908. The determination module 866 may also implement thefunctionality of the terminal 908 relating to the receiving of a pagingrequest. Alternatively or additionally, the memory 964 may comprise areceiving module 967 implementing the latter described receivingfunctionality. The determination module 966 may also implement thefunctionality of the terminal 908 relating to the sending of the supportindication alone or together with a registration request, a pagingrejection in which the call continuity indication or the errorindication may be included and a paging response. Alternatively oradditionally, the memory 964 may comprise a sending module 968implementing the latter described sending functionality. Further, thememory 964 may also comprise a control module 970 for implementingvarious control functionalities of the terminal 908, for example forcontrolling operations related to sending feedback messages or receivingcontrol messages via the interface 962.

It is to be understood that the structures as illustrated in FIGS. 8, 9are merely schematic and that the terminal 808, 908 may actually includefurther components which, for the sake of clarity, have not beenillustrated, for example, further interfaces or processors. Also, it isto be understood that the memory 864, 964 may include further types ofprogram code modules, which have not been illustrated, for example,program code modules for implementing known functionalities of aterminal. According to some embodiments, a computer program may beprovided. The computer program may be embodied as or may comprise theabove program code. The computer program may be executable by the one ormore processors 860, 960. The execution of the computer program by theone or more processors 860, 960 may cause the terminal 808, 908 toperform a method described above and/or below. According to someembodiments, also a computer program product may be provided forimplementing functionalities of the terminal 808, 908, for example, inthe form of a medium storing the program code and/or other data to bestored in the memory 894, 964.

In the following, a communication system according to an embodiment willbe described. The communication system comprises at least one of thecontrol node 104, 604, 704 described above with reference to FIGS. 1 to7 and/or below with reference to FIGS. 10, 11, and a terminal 108, 808,908 described above with reference to FIGS. 1 to 6 and 8, 9 and/or belowwith reference to FIGS. 10, 11.

Referring to FIG. 10, methods, nodes, a terminal, a communication systemand computer programs to be usable in association with terminating acircuit switched signaling service to the terminal via a circuitswitched access of a mobile network according to another embodiment willbe described. The terminal may be referred to the following as userequipment UE and may be labeled in FIG. 10 by a reference numeral 108for ease of explanation. The abbreviation CS stands for circuitswitched. The first control node 102, 602 described above may correspondin the following to the MSC. For ease of explanation, the MSC may belabeled in FIG. 10 by a reference numeral 602. The second control node104, 604, 704 described above may correspond in the following to theMME. For ease of explanation, the MME may be labeled in FIG. 10 by areference numeral 604. The access node 106 described above maycorrespond in the following to the eNodeB.

A basic concept of the embodiment is as follows: Correcting the handlingof NW-initated CS service such that either in a first alternative called(Alt 1) the network does not page the UE or in a second alternativecalled (Alt 2) the UE can reject the paging in case of an ongoing IMSvoice call and that the UE can decide whether SRVCC should be applied ornot. The embodiment may enable that during network-initiated CS serviceslike USSD, when an IMS call is ongoing, the IMS call is not interrupted.

The embodiment may relate to a handling of terminating CS servicesduring IMS Call. Currently it is specified in 3GPP TS 23.272 V11.4.0(2013-03) that the UE performs CS fallback in case of a NW-initiated CSservice other than voice or LR, even if there is an IMS voice callongoing. Only for MT-LR the handling in case of an ongoing IMS voicecall is described. However, this may cause an interruption of an IMSvoice call in case of a NW-initiated CS services and this is not wanted.Therefore, as mentioned above, correcting the handling of NW-initated CSservice is performed such that either (Alt 1) the network does not pagethe UE or (Alt 2) the UE can reject the paging in case of an ongoing IMSvoice call and that the UE can decide whether SRVCC should be applied ornot. Therefore the IMS call may be terminated during network-initated CSservice like USSD.

A NW-Initiated CS Services procedure will be described in the following.

In a step 1, MSC/VLR receives a trigger for a NW-Initiated CS procedure.

In a step 2, MSC/VLR sends Paging message to MME. For call independentsupplementary service, the Paging message must include the SS serviceID.

In a step 3, if the MME did not return the “SMS-only” indication to theUE during Attach or Combined TA/LA Update procedures, and (Alt 1) ifthere is no QCI=1 bearer for the UE, then the MME sends Paging(parameters as specified in TS 23.401 [2], CN Domain Indicator) messageto UE. For call independent supplementary service the Paging message mayinclude the SS service ID. SS service ID is used to indicate the type ofthe supplementary service (e.g. USSD) to the UE. The SS service ID mustbe included in CS Page if UE is in active mode.

If the MME returned the “SMS-only” indication to the UE during Attach orCombined TA/LA Update procedures, or if there is a QCI=1 bearer for theUE, the MME shall not send the Paging to the UE, and the MME sends CSPaging Reject towards MSC to stop CS Paging procedure and this CSFBprocedure stops.

In a step 4, (Alt 2) if the UE is not engaged in an IMS voice (or video)call (active or alerting phase), then the mobile terminating callprocedure then takes place as specified in clause 7 “Mobile TerminatingCall Procedure” of TS 23.272 V11.4.0 (2013-03). The IMS layer in the UEneeds either to inform the NAS layer in the UE that an IMS voice (orvideo) call is ongoing or the NAS layer, when receiving the paging,needs to query the IMS layer.

If the UE is engaged in an IMS voice (or video) call, and then the UEmay decide to reject the paging with an appropriate error code such thatthe MME is informed and continues with step 3 as described in clause8.3.2.2 of TS 23.272 V11.4.0 (2013-03), i.e., SRVCC is initiated and theMSC is informed to continue the applicable CS procedure in GERAN/UTRAN.

It is noted that this implies that the same MSC is used for SRVCC andfor CSFB.

If the UE does not want to perform SRVCC to receive the NW-initiated CSservice, then the UE rejects the paging with an appropriate error codesuch that the MME does not continue with step 3 as described in clause8.3.2.2 of TS 23.272 V11.4.0 (2013-03) and instead only informs the MSCabout the paging error or rejection.

If receiving a paging with an SS service ID for which an IMS service isalso available (e.g. support of terminating IMS USSD), and the UE hasn'tregistered yet for that service, then the UE may perform IMSregistration indicating support for this IMS service. The network shouldthen use the IMS service instead of the CS service for termination.

It is noted that (Alt 1) and (Alt 2) can be combined by adding a timerand a counter to Alt 1—if within a defined time the defined numbers ofterminating NW-initated CS service requests is counted, then paging issend to the UE and Alt 2 is initiated.

In a step 5, once the paging is successfully returned to MSC, theapplicable CS procedures continues, e.g. for Supplementary Service asspecified in specifications such as TS 23.090 mentioned above.

Referring to FIG. 11, methods, nodes, a terminal, a communication systemand computer programs to be usable in association with terminating acircuit switched signaling service to the terminal via a circuitswitched access of a mobile network according to another embodiment willbe described. The terminal may be referred to the following as userequipment UE and may be labeled in FIG. 11 by a reference numeral 108for ease of explanation. The abbreviation CS stands for circuitswitched. The first control node 102, 602 described above may correspondin the following to the MSC. For ease of explanation, the MSC may belabeled in FIG. 11 by a reference numeral 602. The second control node104, 604, 704 described above may correspond in the following to theMME. For ease of explanation, the MME MSC may be labeled in FIG. 11 by areference numeral 602. The access node 106 described above maycorrespond in the following to the eNodeB. For ease of explanation, theeNodeB may be labeled in FIG. 11 by a reference numeral 1106.

The embodiment relates to handling of terminating CS services during IMSCall. Currently it is specified in TS 23.272 V11.4.0 (2013-03) that theUE performs CS fallback in case of a NW-initiated CS service other thanvoice, even if there is an IMS voice call ongoing. Only for MT-LR thehandling in case of an ongoing IMS voice call is described (and SRVCC isinitiated in this case). However, performing CS fallback in case an IMSvoice call is ongoing without initiating SRVCC will cause aninterruption of this IMS voice call and this is not wanted. Accordingly,the embodiment suggests correcting the handling of NW-initated CSservice such that the UE can reject the paging in case of an ongoing IMSvoice call and that the UE can decide whether SRVCC should be applied ornot. Therefore, the IMS call is terminated during network-initated CSservice like USSD.

NW-Initiated CS Service procedures if UE is in IMS VoIP session will bedescribed in the following.

In a step 1, MSC/VLR receives a trigger for a NW-Initiated CS procedure.

In a step 1a., the MSC responds by sending a Paging Request to the MMEover a SGs interface. For call independent supplementary service, thePaging message may include the SS service ID. The MME has an establishedS1 connection for IMS VoIP session.

If the MME did not return the “SMS-only” indication to the UE duringAttach or Combined TA/LA Update procedures, the MME sends Paging(parameters as specified in TS 23.401 mentioned above, CN DomainIndicator) message to UE. For call independent supplementary service thePaging message may include the SS service ID. SS service ID is used toindicate the type of the supplementary service to the UE. The SS serviceID is only included in CS Page if UE is in active mode.

If the MME returned the “SMS-only” indication to the UE during Attach orCombined TA/LA Update procedures, the MME shall not send the Paging tothe UE, and the MME sends CS Paging Reject towards MSC to stop CS Pagingprocedure and this CSFB procedure stops.

The eNodeB forwards the paging message to the UE.

In a step 1b., UE sends an Extended Service Request (Reject or Accept)message to the MME for mobile terminating CS Fallback. The ExtendedService Request message is encapsulated in RRC and S1-AP messages.

In a step 1c., upon receiving the Extended Service Request (Reject) formobile terminating CS Fallback, the MME sends Paging Reject towards MSCto stop CS Paging procedure and this CSFB procedure stops. Correspondingerror handling is returned to the GMLC as specified in TS 23.271 V11.2.0(2013-03).

In a step 1d., MME sends an S1-AP Request message to eNodeB thatincludes the UE Radio Capabilities and a CS Fallback Indicator. Thismessage indicates to the eNodeB that the UE should be moved toUTRAN/GERAN.

In a step 1e., the eNodeB shall reply with S1-AP Response message.

In a step 2, these steps are performed as defined in clause 7.3 of TS23.272 V11.4.0 (2013-03) for PS handover supported case and clause 7.4TS 23.272 V11.4.0 (2013-03) for No PS handover supported case.

In a step 3, based on UE measurement reports and CS Fallback Indicatorin step 1d, the source E UTRAN decides to trigger an SRVCC handover toUTRAN/GERAN. Continuous SRVCC procedures as specified in TS 23.216V11.0.0 (2012-09), clause 6.2.2.2 for PS handover supported case andclause 6.2.2.1a for No PS HO supported case are performed.

In a step 4, after receiving Relocation/Handover Complete message fromthe RNS/BSS in step 3, the applicable CS procedures continues, e.g. forSupplementary Service as specified in specifications such as TS 23.090mentioned above.

It is noted that when SRVCC capable UE is in active mode with an IMSVoIP session but the network does not support SRVCC, MME sends PagingReject towards MSC and this CSFB procedure stops. This is based on thebearer information at MME indicating UE has IMS VoIP session, i.e. EPSbearer with QCI=1.

In the following, further embodiments will be described.

In an embodiment 1, a method to be used in association with terminatinga circuit switched signaling service to a terminal 108, 808, 908 via acircuit switched access of a mobile network 100, 600 is provided, thesignaling service being different from a voice call via the circuitswitched access and from a mobile terminating location request service,a call via an internet protocol domain of the mobile network 100, 600and a packet switched access of the mobile network 100, 600 beingestablished for the terminal 108, 808, 908, the method being performedby a control node 104, 604, 704 of the mobile network 100, 600 andcomprising: receiving 112, 512 a, 512 b a paging request for paging theterminal 108, 808, 908 via the packet switched access, the pagingrequest being for the circuit switched signaling service, determining118, 518 a, 518 b whether a call via the internet protocol domain andthe packet switched access is established for the terminal 108, 808, 908depending on the received paging request, and sending 120 a, 520 a apaging rejection for rejecting the received paging request depending onthe call via the internet protocol domain and the packet switched accessbeing established for the terminal 108, 808, 908 and sending 120 b, 220b, 520 b, via the packet switched access, a paging request for pagingthe terminal 108, 808, 908 depending on the call via the internetprotocol domain and the packet switched access being not established forthe terminal 108, 808, 908.

In an embodiment 2, the method according to embodiment 1 is provided,wherein the step 118, 518 a, 518 b of determining comprises: determiningwhether bearer information is available in the control node 104, 604,704, the bearer information indicating a call via the internet protocoldomain and the packet switched access being established for the terminal108, 808, 908, wherein the step 120 a, 520 a of sending the pagingrejection is performed depending on the bearer information beingavailable in the control node 104, 604, 704, wherein the step 120 b, 220b, 520 b of sending the paging request is performed depending on thecontrol node 104, 604, 704 being free of the bearer information.

In an embodiment 3, the method according to embodiment 1 or 2 isprovided, the method further comprising: determining 116, 516 a, 516 bwhether the control node 104, 604, 704 has sent a fallback indication tothe terminal 108, 808, 908, the fallback indication indicating aterminal support of a circuit switched fall back procedure for a circuitswitched short messaging service, wherein the step 120 a, 520 a ofsending the paging rejection is performed depending on the control node104, 604, 704 having sent the fallback indication, wherein the step 120b, 220 b, 520 b of sending the paging request via the packet switchedaccess is performed depending on the control node 104, 604, 704 havingnot sent the fallback indication.

In particular, the fallback indication may be embodied as the “SMS only”indication explained above.

In an embodiment 4, the method according to any one of embodiments 1 to3 is provided, the method further comprising: starting 548 a timer and acounter in the control node 104, 604, 704 in response to the receivedpaging request, the timer running for a predetermined time interval, thecounter counting a number of paging requests received by the controlnode 104, 604, 704, receiving 512 a, 512 b at least a further pagingrequest for paging the terminal 108, 808, 908 via the packet switchedaccess, and sending 520 b, via the packet switched access, a furtherpaging request depending on a counted number of received paging requestsbeing equal to or exceeding a predetermined number of paging requestswithin the predetermined time interval.

In an embodiment 5, the method according to any one of embodiment 1 to 4is provided, wherein at least one of the received paging request, thereceived at least further paging request, the sent paging request andthe sent further paging request comprises an identification of thecircuit switched signaling service, particularly a SS service ID.

In an embodiment 6, a method to be used in association with terminatinga circuit switched signaling service to a terminal 108, 808, 908 via acircuit switched access of a mobile network 100, 600 is provided, thesignaling service being different from a voice call via the circuitswitched access and from a mobile terminating location request service,a call via an internet protocol domain of the mobile network 100, 600and a packet switched access of the mobile network 100, 600 beingestablished for the terminal 108, 808, 908, the method being performedby the terminal 108, 808, 908 and comprising: receiving 120 b, 220 b,520 b, via the packet switched access, a paging request for paging theterminal 108, 808, 908, the paging request being for the circuitswitched signaling service, determining 222 whether a call via theinternet protocol domain and the packet switched access is establishedfor the terminal 108, 808, 908 depending on the received paging request,and sending 228 a, via the packet switched access, a paging error forindicating an unsuccessful handling of the paging request by theterminal 108, 808, 908 depending on the call via the internet protocoldomain and the packet switched access being established for the terminal108, 808, 908 and sending 228 b a paging response for indicating asuccessful handling of the paging request by the terminal 108, 808, 908depending on the call via the internet protocol domain and the packetswitched access being not established for the terminal 108, 808, 908.

In an embodiment 7, the method according to embodiment 6 is provided,wherein the step 222 of determining comprises using information providedfrom a first protocol layer in the terminal 108, 808, 908, particularlyan Internet Protocol Multimedia Subsystem layer, to a lower secondprotocol layer in the terminal 108, 808, 908, particularly a Non AccessStratum layer.

In an embodiment 8, the method according to embodiment 7 is provided,wherein the information is provided from the first protocol layer uponrequest from the lower second protocol layer.

In an embodiment 9, the method according to any one of embodiments 6 to8 is provided, the method further comprising at least one of:determining 224 whether the terminal 108, 808, 908 will receive thecircuit switched signaling service, and determining 226 whether theterminal 108, 808, 908 will perform a call continuity procedure for theestablished call from the packet switched access to the circuit switchedaccess, wherein the step 228 a of sending the paging error is performeddepending on the terminal 108, 808, 908 will receive the circuitswitched signaling service and/or depending on the terminal 108, 808,908 will perform the call continuity procedure, particularly an errorcode of a first type.

In an embodiment 10, the method according to any one of embodiments 6 to9 is provided, wherein the paging error comprises a call continuityindication indicating to initiate, for the established call of theterminal (108, 808, 908), a call continuity procedure from the packetswitched access to the circuit switched access.

In an embodiment 11, the method according to embodiment 9 or 10 isprovided, the method further comprising: performing 340 the callcontinuity procedure for the established call of the terminal 108, 808,908 subsequent to an access node 106 of the mobile network 100, 600requesting to perform the call continuity procedure.

In an embodiment 12, the method according to any one of embodiments 6 to11 is provided, wherein the step 228 a of sending the paging error isperformed depending on the terminal 108, 808, 908 will not receive thecircuit switched signaling service and/or depending on the terminal 108,808, 908 will not perform the call continuity procedure, and/or whereinthe sent paging error comprises an error indication indicating theunsuccessful handling of the paging request by the terminal 108, 808,908, particularly an error code of a second type.

In an embodiment 13, the method according to any one of embodiments 6 to12 is provided, the method further comprising: determining 230 whether asignaling service via the internet protocol domain is available for theterminal 108, 808, 908, the signaling service via the internet protocoldomain corresponding to the circuit switched signaling service to beterminated, and sending 232, via the packet switched access, a supportindication indicating a terminal support of the signaling service viathe internet protocol domain depending on the signaling service via theinternet protocol domain being available for the terminal 108, 808, 908.

In an embodiment 14, the method according to embodiment 13 is provided,the method further comprising: determining 234 whether the terminal 108,808, 908 is registered in the signaling service via the internetprotocol domain, wherein the support indication is sent together with aregistration request for registering in the signaling service via theinternet protocol domain depending on the terminal 108, 808, 908 beingnot registered in the signaling service via the internet protocoldomain, wherein the support indication is sent without the registrationrequest for registering in the signaling service via the internetprotocol domain depending on the terminal 108, 808, 908 being registeredin the signaling service via the internet protocol domain.

In an embodiment 15, a method to be used in association with terminatinga circuit switched signaling service to a terminal 108, 808, 908 via acircuit switched access of a mobile network 100, 600 is provided, thesignaling service being different from a voice call via the circuitswitched access and from a mobile terminating location request service,a call via an internet protocol domain of the mobile network 100, 600and a packet switched access of the mobile network 100, 600 beingestablished for the terminal 108, 808, 908, the method being performedby the terminal 108, 808, 908 and comprising: receiving 120 b, 220 b apaging request for paging the terminal 108, 808, 908 via the packetswitched access, the paging request being for the circuit switchedsignaling service, determining 230 whether a signaling service via theinternet protocol domain is available for the terminal 108, 808, 908depending on the received paging request, the signaling service via theinternet protocol domain corresponding to the circuit switched signalingservice, and sending 232, via the packet switched access, a supportindication indicating a terminal support of the signaling service viathe internet protocol domain depending on the signaling service via theinternet protocol domain being available for the terminal 108, 808, 908.

In an embodiment 16, the method according to embodiment 15 is provided,the method further comprising: sending 228 a, via the packet switchedaccess, a paging error for indicating an unsuccessful handling of thepaging request by the terminal 108, 808, 908 depending on the receivedpaging request.

In an embodiment 17, the method according to embodiment 15 or 16 isprovided, the method further comprising: determining 222 whether a callvia the internet protocol domain and the packet switched access isestablished for the terminal 108, 808, 908 depending on the receivedpaging request, wherein the step 229 a of sending the paging error isperformed depending on the call via the internet protocol domain and thepacket switched access being established for the terminal 108, 808, 908.

In an embodiment 18, a control node 104, 604, 704 for a mobile network100, 600 is provided, the control node 104, 604, 704 being usable inassociation with terminating a circuit switched signaling service to aterminal 108, 808, 908 via a circuit switched access of a mobile network100, 600, the signaling service being different from a voice call viathe circuit switched access and from a mobile terminating locationrequest service, a call via an internet protocol domain of the mobilenetwork 100, 600 and a packet switched access of the mobile network 100,600 being established for the terminal 108, 808, 908, the control node104, 604, 704 being adapted to: receive a paging request for paging theterminal 108, 808, 908 via the packet switched access, the pagingrequest being for the circuit switched signaling service, determinewhether a call via the internet protocol domain and the packet switchedaccess is established for the terminal 108, 808, 908 depending on thereceived paging request, and send a paging rejection for rejecting thereceived paging request depending on the call via the internet protocoldomain and the packet switched access being established for the terminal108, 808, 908 and send, via the packet switched access, a paging requestfor paging the terminal 108, 808, 908 depending on the call via theinternet protocol domain and the packet switched access being notestablished for the terminal 108, 808, 908.

In an embodiment 19, the control node according to embodiment 18 isprovided, adapted to perform the method according to any one ofembodiments 2 to 5.

In an embodiment 20, a terminal 108, 808, 908 to be usable inassociation with terminating a circuit switched signaling service to theterminal 108, 808, 908 via a circuit switched access of a mobile network100, 600 is provided, the signaling service being different from a voicecall via the circuit switched access and from a mobile terminatinglocation request service, a call via an internet protocol domain of themobile network 100, 600 and a packet switched access of the mobilenetwork 100, 600 being established for the terminal 108, 808, 908, theterminal 108, 808, 908 being adapted to: receive, via the packetswitched access, a paging request for paging the terminal 108, 808, 908,the paging request being for the circuit switched signaling service,determine whether a call via the internet protocol domain and the packetswitched access is established for the terminal 108, 808, 908 dependingon the received paging request, and send, via the packet switchedaccess, a paging error for indicating an unsuccessful handling of thepaging request by the terminal 108, 808, 908 depending on the call viathe internet protocol domain and the packet switched access beingestablished for the terminal 108, 808, 908 and send a paging responsefor indicating a successful handling of the paging request by theterminal 108, 808, 908 depending on the call via the internet protocoldomain and the packet switched access being not established for theterminal 108, 808, 908.

In an embodiment 21, the terminal 108, 808, 908 according to embodiment20 is provided, adapted to perform the method according to any one ofembodiments 7 to 14.

In an embodiment 22, a terminal 108, 808, 908 to be usable inassociation with terminating a circuit switched signaling service to theterminal 108, 808, 908 via a circuit switched access of a mobile network100, 600 is provided, the signaling service being different from a voicecall via the circuit switched access and from a mobile terminatinglocation request service, a call via an internet protocol domain of themobile network 100, 600 and a packet switched access of the mobilenetwork 100, 600 being established for the terminal 108, 808, 908, theterminal 108, 808, 908 being adapted to: receive a paging request forpaging the terminal 108, 808, 908 via the packet switched access, thepaging request being for the circuit switched signaling service,determine whether a signaling service via the internet protocol domainis available for the terminal 108, 808, 908 depending on the receivedpaging request, the signaling service via the internet protocol domaincorresponding to the circuit switched signaling service, and send, viathe packet switched access, a support indication indicating a terminalsupport of the signaling service via the internet protocol domaindepending on the signaling service via the internet protocol domainbeing available for the terminal 108, 808, 908.

In an embodiment 23, the terminal 108, 808, 908 according to embodiment22 is provided, adapted to perform a method according to any oneembodiments 7, 8, 9, 10, 11, 12, 14, 16 and 17.

In an embodiment 24, a communication system for terminating a circuitswitched signaling service to the terminal 108, 808, 908 via a circuitswitched access of a mobile network 100, 600 is provided, thecommunication system comprising at least one of a control node accordingto embodiment 18 or 19 and a terminal according to any one ofembodiments 20 to 23.

In an embodiment 25, a computer program, which being executed byprocessor, is adapted to perform a method according to any one ofembodiments of 1 to 17.

It is noted that steps of one of the above described method embodimentsalso apply to the respective other methods embodiments, the controlnodes, the terminal, the communication system, and the computerprograms.

Modifications and other embodiments of the disclosed embodiments willcome to mind to one skilled in the art having the benefit of theteachings presented in the foregoing descriptions and the associateddrawings. Therefore, it is to be understood that the embodiments are notto be limited to the specific embodiments disclosed and thatmodifications and other embodiments are intended to be included withinthe scope of this disclosure. Although specific terms may be employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation. The description of the embodiments withreference to 3GPP may not exclude the described embodiments beingapplicable in other communication networks and/or technologies, thenetworks and/or technologies being different from 3GPP.

The invention claimed is:
 1. A method to be used in association withterminating a circuit switched signaling service to a terminal via acircuit switched access of a mobile network, the signaling service beingdifferent from a voice call via the circuit switched access and from amobile terminating location request service, wherein a call via aninternet protocol domain of the mobile network and a packet switchedaccess of the mobile network is or is being established for theterminal, the method comprising: the terminal receiving a paging requestfor paging the terminal via the packet switched access, the pagingrequest being for the circuit switched signaling service; the terminaldetermining whether a packet switched signaling service that correspondsto the circuit switched signaling service is available via the internetprotocol domain for the terminal; and the terminal sending, via thepacket switched access, a support indication indicating a support forthe packet switched signaling service via the internet protocol domaindepending on the packet switched signaling service via the internetprotocol domain being available for the terminal.
 2. The method of claim1, further comprising: in response to the paging request, the terminalsending, via the packet switched access, not only the supportindication, but also a paging rejection for rejecting the paging requestdepending on the received paging request.
 3. The method of claim 1,further comprising the terminal sending, via the packet switched access,a paging rejection for rejecting the paging request depending on aresult of the step of determining.
 4. The method of claim 1, furthercomprising the terminal determining whether a call via the internetprotocol domain and the packet switched access is or is beingestablished for the terminal depending on the received paging request;and the terminal sending a paging rejection depending on the call viathe internet protocol domain and the packet switched access is or isbeing established for the terminal.
 5. The method of claim 1, furthercomprising the terminal receiving, during an attach procedure or acombined tracking area/location area (TA/LA) update procedure, atermination indication transmitted by a mobility management node,wherein the termination indication indicates that a CS short messagingservice (SMS) is terminatable to the terminal via the packet switchedaccess.
 6. The method according to claim 5, wherein the terminationindication is an SMS-only indication.
 7. A terminal to be usable inassociation with terminating a circuit switched signaling service to theterminal via a circuit switched access of a mobile network, thesignaling service being different from a voice call via the circuitswitched access and from a mobile terminating location request service,wherein a call via an internet protocol domain of the mobile network anda packet switched access of the mobile network is or is beingestablished for the terminal, the terminal being adapted to: receive apaging request for paging the terminal via the packet switched access,the paging request being for the circuit switched signaling service,determine whether a packet switched signaling service that correspondsto the circuit switched signaling service is available via the internetprotocol domain for the terminal, and send, via the packet switchedaccess, a support indication indicating a support for the packetswitched signaling service via the internet protocol domain depending onthe packet switched signaling service via the internet protocol domainbeing available for the terminal.
 8. The terminal of claim 7, whereinthe terminal is further adapted to send, via the packet switched access,a paging rejection for rejecting the paging request depending on thereceived paging request.
 9. The terminal of claim 7, wherein theterminal is further adapted to send, via the packet switched access, apaging rejection for rejecting the paging request depending on a resultof the step of determining.
 10. The terminal of claim 7, wherein theterminal is further adapted to: determine whether a call via theinternet protocol domain and the packet switched access is or is beingestablished for the terminal depending on the received paging request;and send a paging rejection depending on the call via the internetprotocol domain and the packet switched access is or is beingestablished for the terminal.
 11. A computer program product comprisinga non-transitory computer readable medium, wherein the non-transitorycomputer readable medium stores: instructions for processing a receivedpaging request for paging the terminal via the packet switched access,the paging request being for the circuit switched signaling service;instructions for determining whether a packet switched signaling servicethat corresponds to the circuit switched signaling service is availablevia the internet protocol domain for the terminal; and instructions forsending, via the packet switched access, a support indication indicatinga support for the packet switched signaling service via the internetprotocol domain depending on the packet switched signaling service viathe internet protocol domain being available for the terminal.
 12. Thecomputer program product of claim 11, wherein the non-transitorycomputer readable medium further stores: instructions for sending, viathe packet switched access, a paging rejection for rejecting the pagingrequest depending on the received paging request.
 13. The computerprogram product of claim 11, wherein the non-transitory computerreadable medium further stores instructions for sending, via the packetswitched access, a paging rejection for rejecting the paging requestdepending on a result of the step of determining.
 14. The computerprogram product of claim 11, wherein the non-transitory computerreadable medium further stores: instructions for determining whether acall via the internet protocol domain and the packet switched access isor is being established for the terminal depending on the receivedpaging request; and instructions for sending a paging rejectiondepending on the call via the internet protocol domain and the packetswitched access is or is being established for the terminal.